The present invention relates to a new and improved coupling assembly and more specifically to a coupling assembly which includes a brake assembly and a clutch assembly which are actuated to control the rotation of an output member.
A coupling assembly having a clutch assembly and a brake assembly which are sequentially actuated to control the rotation of an output member is disclosed in U.S. Pat. No. 4,807,731 issued Feb. 28, 1989 and entitled "Clutch and Brake Assembly". Coil springs resiliently bias the brake assembly toward an engaged condition. Fluid pressure is conducted to a first chamber to operate the brake assembly from the engaged condition to a disengaged condition against the influence of the coil springs. The fluid pressure in the first chamber also operates the clutch assembly from a disengaged condition to an engaged condition.
When the clutch assembly disclosed in the aforementioned U.S. Pat. No. 4,807,731 is to be disengaged and the brake assembly engaged, the fluid pressure which previously operated the clutch assembly to the engaged condition is vented to the atmosphere. The coil springs then operate the brake assembly to an engaged condition. Fluid pressure is conducted to a second chamber to assist the coil springs in disengaging the clutch assembly and engaging the brake assembly.
Coupling assemblies having this general construction have been used with machines which are operated at relatively high rates and particularly with can forming machines. It has previously been suggested that quick release exhaust valves could be utilized in association with the coupling chamber which is pressurized to operate the brake assembly to the disengaged condition and to engage the clutch assembly. Thus, U.S. Pat. No. 4,874,068 issued Oct. 17, 1989 and entitled "Clutch and Brake Rapid Exhaust Manifold" indicates that a coupling assembly can be used with a machine having operating rates as high as 300 to 400 cycles per minute when quick release valve assemblies are utilized to effect rapid depressurization of the chamber which is pressurized to operate the clutch assembly to the engaged condition and the brake assembly to the disengaged condition.
It has been found that the coupling assemblies of the prior art operate satisfactorily in association with machines which operate at rates as high as 300 to 400 cycles per minute. It is believed that premature failure of machines which have higher operating rates may be caused by the application of excessive torque to the machine input shaft and coupling when the brake assembly is operated from the disengaged condition to the engaged condition under the combined influence of the biasing springs and fluid pressure in the manner disclosed in the aforementioned U.S. Pat. No. 4,807,731. Under certain circumstances, the application of excessive brake torque can result in breakage of the input shaft to a machine which is driven through the coupling assembly.